Method and device for terminal attaching and creating home-routed pdu session in roaming environment supporting network slice

ABSTRACT

The present disclosure relates to a 5G or pre-5G communication system for supporting a data transmission rate higher than that of a 4G communication system such as LTE. According to one embodiment of the present invention, a method in a roaming environment supporting a network slice is provided. The method comprises the steps of: receiving, from a terminal, a first packet data unit (PDU) session request message including slice assistance information indicating the properties of a service the terminal intends to use; transmitting, to a network function (NF) repository function, a first discovery request message including a home public land mobile network (PLMN) ID of the terminal and the slice assistance information; and receiving, from the NF repository function, a first discovery response message including a session management network function (SM NF) address of the home PLMN. The SM NF is selected, on the basis of the slice assistance information, from SM NFs of a PLMN associated with the home PLMN ID.

TECHNICAL FIELD

The disclosure relates to a mobile communication system. Particularly,the disclosure relates to, when a terminal performs roaming to a networkthat supports a network slice, a method for the terminal to attach tothe network and a method for the terminal to generate a packet data unit(PDU) session for providing home-routed traffic.

BACKGROUND ART

In order to satisfy the increasing demands of radio data traffic afterthe commercialization of a 4G communication system, efforts have beenmade to develop an advanced 5G communication system or a pre-5Gcommunication system. For this reason, the 5G communication system orthe pre-5G communication system is also referred to as a beyond-4Gnetwork communication system or a post-LTE system. In order toaccomplish a higher data transfer rate, the implementation of the 5Gcommunication system in a super-high frequency (mmWave) band (e.g.,about a 60 GHz band) is being considered. Also, in order to obviate apropagation loss of a radio wave and increase a delivery distance of aradio wave in the super-high frequency band, discussions for the 5Gcommunication system are underway about various techniques such as abeamforming, a massive MIMO, a full dimensional MIMO (FD-MIMO), an arrayantenna, an analog beam-forming, and a large scale antenna.Additionally, for an improvement in network of the 5G communicationsystem, technical developments are being made in an advanced small cell,a cloud radio access network (cloud RAN), an ultra-dense network, adevice to device (D2D) communication, a wireless backhaul, a movingnetwork, a cooperative communication, coordinated multi-points (COMP), areception-end interference cancellation, and the like. Also, in the 5Gcommunication system, a hybrid FSK and QAM modulation (FQAM) and asliding window superposition coding (SWSC) are developed as advancedcoding modulation (ACM) schemes, and a filter bank multi carrier (FBMC),a non-orthogonal multiple access (NOMA), and a sparse code multipleaccess (SCMA) are also developed as advanced access techniques.

Meanwhile, one of new structural features of the 5G network is theintroduction of network slicing technology for radio access network(RAN) and core network (CN) structures. The network slicing technologybundles network resources and network functions into one independentslice for each individual service. Using the network slicing technologymakes it possible to apply attributes such as isolation, customization,or independent management and orchestration of network system functionsand resources to a mobile communication network structure. Therefore, anetwork operator can independently allocate network resourcesspecialized to each service and user, and can independently and flexiblyprovide services by selecting and combining network functions of the 5Gsystem according to criteria such as service, user, and business model.

One of technical issues (work tasks) essential to the development of anetwork slicing structure is network slicing roaming support. Thedisclosure describes network functions required in a home network and avisited network in order to realize the network slicing roaming support,that is, in order to support roaming of a terminal (UE).

DISCLOSURE OF INVENTION Technical Problem

The disclosure provides a method for a terminal to access an operator'snetwork that supports a network slice.

The disclosure provides a method for connecting a terminal-subscribedmobile communication operator (i.e., a home network) and a mobilecommunication operator of a visited area (i.e., a visited network) whenthe terminal attaches to an operator's network supporting a networkslice and receive a service in a mobile communication system.

The disclosure provides a method for generating a packet data unit (PDU)session for serving home-routed traffic to a roaming terminal.

Solution to Problem

According to an embodiment of the disclosure, provided is a method in aroaming environment that supports a network slice. The method includesreceiving, from a terminal by a serving common control plane networkfunction (serving CCNF), a first packet data unit (PDU) session requestmessage containing slice assistance information indicating acharacteristic of a service to be used by the terminal; transmitting, toa network function (NF) repository function, a first discovery requestmessage containing an ID of a home public land mobile network (homePLMN) of the terminal and the slice assistance information; andreceiving, from the NF repository function, a first discovery responsemessage containing an address of a session management network function(SM NF) of the home PLMN. The SM NF of the home PLMN is selected fromamong SM NFs of a PLMN associated with the home PLMN ID, based on thehome PLMN ID and the slice assistance information.

According to another embodiment of the disclosure, a common controlplane network function (CCNF) of a visited public land mobile network(visited PLMN) is provided in a roaming environment that supports anetwork slice. The CCNF includes a transceiver transmitting andreceiving signals to and from a terminal and a network function (NF)repository function; and a controller connected to the transceiver. Thecontroller is configured to control the transceiver to receive, from theterminal, a first packet data unit (PDU) session request messagecontaining slice assistance information indicating a characteristic of aservice to be used by the terminal, to control the transceiver totransmit, to the NF repository function, a first discovery requestmessage containing an ID of a home PLMN of the terminal and the sliceassistance information, and to control the transceiver to receive, fromthe NF repository function, a first discovery response messagecontaining an address of a session management network function (SM NF)of the home PLMN. The SM NF of the home PLMN is selected from among SMNFs of a PLMN associated with the home PLMN ID, based on the home PLMNID and the slice assistance information.

According to still another embodiment of the disclosure, provided is amethod for generating a home-routed packet data unit (PDU) session by aterminal in a roaming environment that supports a network slice. Themethod includes transmitting, to a common control plane network function(CCNF) of a visited public land mobile network (visited PLMN), a firstPDU session request message containing slice assistance informationindicating a characteristic of a service to be used by the terminal; andreceiving, from the CCNF of the visited PLMN, a first PDU sessionresponse message containing an Internet protocol (IP) address of theterminal. The IP address of the terminal is acquired from a sessionmanagement network function (SM NF) of a home PLMN in response to athird PDU session request message containing an ID of the terminal, andthe SM NF of the home PLMN is selected from among SM NFs of a PLMNassociated with a home PLMN ID, based on the home PLMN ID and the sliceassistance information.

According to still another embodiment of the disclosure, a terminal isprovided in a roaming environment that supports a network slice. Theterminal includes a transceiver transmitting and receiving signals toand from a common control plane network function (CCNF) of a visitedpublic land mobile network (visited PLMN); and a controller connected tothe transceiver. The controller is configured to control the transceiverto transmit, to the CCNF of the visited PLMN, a first PDU sessionrequest message containing slice assistance information indicating acharacteristic of a service to be used by the terminal, and control thetransceiver to receive, from the CCNF of the visited PLMN, a first PDUsession response message containing an Internet protocol (IP) address ofthe terminal. The IP address of the terminal is acquired from a sessionmanagement network function (SM NF) of a home PLMN in response to athird PDU session request message containing an ID of the terminal, andthe SM NF of the home PLMN is selected from among SM NFs of a PLMNassociated with a home PLMN ID, based on the home PLMN ID and the sliceassistance information.

Advantageous Effects of Invention

When a terminal desires to attach to other operator's network andreceive a service in a roaming environment, it is possible to allocate anetwork slice capable of supporting the service and, through this,provide the service to the terminal.

When home-routed traffic is to be served, it is possible to generate apacket data unit (PDU) session to support a quality of service (QoS)suitable for a terminal and also efficiently operate radio resources andnetwork resources.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example of a core network architecture excluding aterminal and a base station in a network that supports roaming betweenwireless communication systems applying a network slice and also serveshome-routed traffic.

FIG. 2 illustrates a network initial attach and registration procedureof a terminal in a roaming environment to which a network slice isapplied, according to an embodiment of the disclosure.

FIG. 3 illustrates a process in which a terminal generates a PDU sessionfor home-routed traffic in a roaming environment to which a networkslice is applied, according to another embodiment of the disclosure.

FIG. 4 illustrates a process in which a serving CCNF finds anappropriate SM NF through an NF repository function at the SM NFselection step 313 of FIG. 3.

FIG. 5 illustrates a process in which an SM NF1 finds an appropriate UPNF through an NF repository function at the UP NF selection step 315 ofFIG. 3.

FIG. 6 illustrates a process in which an SM NF1 of a visited PLMN findsan appropriate SM NF in a home PLMN through an NF repository function atthe SM NF selection step 317 of the home PLMN of FIG. 3.

FIG. 7 illustrates a process in which an SM NF2 finds an appropriate UPNF through an NF repository function at the UP NF selection step 320 ofFIG. 3.

FIG. 8 illustrates another example of a core network architectureexcluding a terminal and a base station in a network that supportsroaming between wireless communication systems applying a network sliceand also serves home-routed traffic.

FIG. 9 is a diagram illustrating a structure of a terminal according toan embodiment of the disclosure.

FIG. 10 is a diagram illustrating a structure of a CCNF according to anembodiment of the disclosure.

MODE FOR THE INVENTION

Hereinafter, the disclosure will be described in detail with referenceto the accompanying drawings. In the following description of thedisclosure, a description of known functions or configurationsincorporated herein may be omitted to avoid unnecessary obscuration ofthe disclosure. Terms used herein are defined in consideration ofdisclosed functions and may vary based on a user's or operator'sintention or custom. Therefore, the definitions of terms should be madeon the basis of the entire content of this disclosure.

In this disclosure, terms for identifying access nodes, terms forindicating network entities, terms for indicating messages, terms forindicating interfaces between network entities, terms for indicatingvarious types of identification information, and the like are exemplaryfor convenience of description. Therefore, the disclosure is not limitedto terms used herein, and other terms for indicating objects havingequivalent technical meanings may be alternatively used.

Hereinafter, for convenience of description, the terms and names definedin the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE)standard will be used. However, the disclosure is not limited to suchterms and names, and may be equally applied to systems that comply withother standards.

FIG. 1 illustrates an example of a core network architecture excluding aterminal and a base station in a network that supports roaming betweenwireless communication systems applying a network slice and also serveshome-routed traffic.

Referring to FIG. 1, a core network of a wireless communication systemthat supports a network slice is divided into a visited public landmobile network (PLMN) and a home PLMN.

The visited PLMN to which a roaming terminal will attach includes acommon control plane network function (CCNF) 101 and a slice specificcore network function 105 that collects network functions (NFs) relatedto a network slice. The slice specific core network function 105includes slice specific control plane network functions (SSCNF) 107including Slice CP NF_1, . . . , Slice CP NF_n which are control planenetwork functions defined to be used only within a network slice, andslice specific user plane network functions (SSUNF) 108 including SliceUP NF_1, . . . , Slice UP NF_n which are user plane network functionsdefined to be used only within a network slice.

The home PLMN includes a subscriber repository 103 that storessubscription information of a terminal, a home policy control function102 that controls applying a policy in the home PLMN, an applicationfunction (AF) 104 that provides information about the policy to the homepolicy control function 102, and a slice specific core network function106 that collects network functions related to a network slice. Theslice specific core network function 106 includes SSCNF 109 includingSlice CP NF_1, . . . , Slice CP NF_n which are control plane networkfunctions defined to be used only within a network slice, and SSUNF 110including Slice UP NF_1, . . . , Slice UP NF_n which are user planenetwork functions defined to be used only within a network slice.

In addition, the core network may include a visited NF repositoryfunction 112 and a home NF repository function 113, which findappropriate network functions from network functions of the visited PLMNand the home PLMN by request. The visited NF repository function 112 maybe located within the CCNF 101. Also, the home NF repository function113 may operate as a network function instance (NFI) selector locatedwithin the CCNF 101 and performing a function of selecting anappropriate NF from a network slice instance. Although this disclosureuses the term “NF repository function” for convenience of description,this may refer to an NFI selector when a network slice is used. Also,the NF repository function may be referred to as “NF discovery device”or “NF storage device”.

The CCNF 101 is connected to a terminal attaching to the visited PLMNand a base station accessed by the terminal, processes control messagesfor managing the terminal, and manages the mobility of the terminal. Inaddition, the CCNF 101 is connected to the subscriber repository 103located in the home PLMN, receives subscriber related information fromthe subscriber repository 103, and performs authentication of theterminal. Also, the CCNF 101 selects a network slice instance to beprovided to the terminal by using information of the accessing terminal,and selects an appropriate slice CP NF (control plane network function)from the SSCNF 107 belonging to the corresponding network sliceinstance. The CCNF 101 may use the visited NF repository function 112 toselect the appropriate slice CP NF. The slice CP NF selects anappropriate slice UP NF (user plane network function) from the SSUNF 108belonging to the network slice instance. The slice CP NF may use thevisited NF repository function 112 to select the appropriate slice UPNF.

Alternatively, the CCNF 101 may select a network slice instance to beprovided to the corresponding terminal by using information of theterminal, select a slice CP NF from the SSCNF 107 belonging to thecorresponding network slice instance, and select a slice UP NF from theSSUNF 108 belonging to the corresponding network slice instance. Thatis, the CCNF 101 may select both the slice CP NF and the slice UP NF.Also, the CCNF 101 may use the visited NF repository function 110 toselect appropriate slice CP NF and slice UP NF.

The slice CP NF and the slice UP NF selected in the visited PLMN supporta data service in a terminal-belonging network slice through connectionwith a slice CP NF and a slice UP NF selected from the SSCNF 109 and theSSUNF 110 belonging to the home PLMN.

The slice CP NF manages a packet data unit (PDU) session so that theterminal can receive a service through a data network (NW). The slice CPNF may include a session management function for managing transmissionof service data for the terminal by communicating with the selectedslice UP NFs.

The slice UP NF may perform a user plane function of a packet data unitgateway (P-GW) in the Long Term Evolution (LTE) system, such asprocessing packets for user service data through connection with aterminal and a base station.

The above-mentioned functions, for example, the subscriberauthentication function of the CCNF 101, the terminal mobilitymanagement function, the network slice selection function, the functionof selecting the SSCNFs 107 and 109 and the SSUNFs 108 and 110, and thefunction of processing control message through connection with aterminal and a base station, may be defined as individual networkfunctions or as a partly combined network function.

FIG. 2 illustrates a network initial attach and registration procedureof a terminal in a roaming environment to which a network slice isapplied, according to an embodiment of the disclosure.

User equipment (UE) 201, that is, a terminal, transmits at step 211, toa radio access network (RAN) 202, that is, a base station, an initialattach request for requesting registration to attach to a visited PLMNaccording to roaming. The initial attach request may contain UEidentification information, e.g., an international mobile subscriberidentity (IMSI), an international mobile equipment identity code (IMEI),or a temporary ID such as a globally unique temporary identifier (GUTI).In addition, the initial attach request may contain slice selectionassistance information including information about a service registeredin a home PLMN operator by the UE, a service type supporting theservice, a network slice type, or an identifier (ID) indicating anetwork slice.

When the initial attach request is received from the UE 201, the RAN 202selects a default CCNF 203 to process the initial attach request, andtransmits the received initial attach request at step 212. Based on atleast a part of the slice selection assistance information or presetinformation in the visited PLMN, the RAN 202 may select the default CCNF203 to support a network slice or service subscribed by the UE.

When the initial attach request is received from the RAN 202, thedefault CCNF 203 connects with a subscriber repository 205 existing inthe home PLMN to which the UE 201 belongs, performs an authenticationprocedure for determining whether the UE 201 is true UE, and retrievessubscription information (i.e., subscription data) of the UE 201 at step213.

The subscription information of the UE 201 may include information of anetwork slice to which the UE 201 subscribes. Also, at theauthentication and subscription data retrieval step 213, the defaultCCNF 203 may receive, from the subscriber repository 205, information ofdefault data network name (DNN) and information of a DNN list allowedaccording to a service level agreement (SLA) between the visited PLMNand the home PLMN.

Based on the slice selection assistance information received from theRAN 202 at the initial attach request reception step 212 and thesubscription information of the UE 201 received from the subscriberrepository 205 at the authentication and subscription data retrievalstep 213, the default CCNF 203 selects at step 214 a network sliceinstance that can be provided in the visited PLMN.

However, if the default CCNF 103 has difficulty in finding anappropriate network slice instance or if there is a more appropriateCCNF, the default CCNF 103 may forward an attach message to the moreappropriate CCNF so that the more appropriate CCNF will be used as aserving CCNF 103. That is, if the default CCNF is suitable for use, itmay select a network slice instance at step 214. However, if notsuitable or if there is a more appropriate CCNF, the attach message isforwarded to the CCNF at step 215, and the CCNF selects a network sliceinstance at step 216. Hereinafter, the more appropriate CCNF will bedefined and described as CCNF_1 204.

When the default CCNF 203 forwards the attach request message to theCCNF_1 204 at step 215, the serving CCNF is changed. The forwardedattach request message may contain information included in the initialattach request 212, e.g., the UE identification information and theslice selection assistance information. In addition, the forwardedattach request message may contain information acquired at theauthentication and subscription data retrieval step 213, e.g., asubscribed mobility management (MM) context and a subscribed servicemanagement (SM) context. The subscribed SM context may includeinformation about a default DNN and information about an allowed DNNlist.

Alternatively, the CCNF_1 204 may acquire information such as thesubscribed MM context and the subscribed SM context by retrievingsubscription information via connection with the subscriber repository205. The subscribed SM context may include information about a defaultDNN and information about an allowed DNN list.

Meanwhile, at the network slice instance selection step 216, the CCNF_1204 may select a network slice that can be provided by the visited PLMN,based on the slice selection assistance information or the likedelivered through the attach request step 215. The CCNF_1 204 allocatesa temporary ID of the UE, inserts information about a service agreed inthe network, e.g., agreed slice selection assistance information, in anattach accept message, and forwards it to the default CCNF 203 at step217. The default CCNF 203 transmits the attach accept message to the RAN202 at step 218, and the RAN 202 transmits the attach accept message tothe UE 201 at step 219.

The above-described attach procedure may be applied even to anon-roaming situation. If information of a default DNN or allowed DNNlist is a DNN value used in the home PLMN when the default CCNF 203 orthe CCNF_1 204 selects a network slice instance in a roaming situation,a home-routed traffic dedicated network slice instance may be selected.

FIG. 3 illustrates a process in which a terminal generates a PDU sessionfor home-routed traffic in a roaming environment to which a networkslice is applied, according to another embodiment of the disclosure.

In order to generate the PDU session in a visited PLMN which is inroaming, the terminal (i.e., UE) 301 transmits a NAS_DU session requestmessage for access to a serving CCNF 302 at step 311. The NAS_DU sessionrequest message includes at least one of a temporary ID which is anidentifier of the UE, requested slice assistance information indicatinga characteristic of the PDU session to be generated by the UE or acharacteristic of a service to be used by the UE, or all or someparameters of a DNN. Like an access point name (APN) in the LTE network,the DNN indicates information of a network from which the UE willreceive an Internet protocol (IP) address to be used. When the DNN isnot contained in the NAS_PDU session request message, a default DNNacquired from subscription information may be used as the DNN.

When the NAS_PDU session request message is received at step 311, theserving CCNF 302 may check subscription information at step 312 in orderto determine whether a service is available for the slice assistanceinformation and DNN requested by the UE. For this, the serving CCNF mayrequest and retrieve the subscription information from a subscriberrepository 309 in a home PLMN. In addition, when a network sliceinstance that allows a service for the requested slice assistanceinformation and DNN is not determined, the serving CCNF 302 may selectan appropriate network slice instance by using a network slice instance(NSI) selector.

The serving CCNF 302 may select at step 313 an SM NF1 303 which is an NFfor session management, based on information about the network sliceinstance selected at the subscription information check step 312.Specifically, the serving CCNF 302 may select the SM NF1 303, based on anetwork function of the serving CCNF 302 and information about a networkslice. Alternatively, the serving CCNF 302 may select the SM NF1 303 byrequesting an entity, such as an NF repository function 305 capable offinding an appropriate network function, to find an appropriate SM NF onthe basis of the selected network slice instance information. A methodfor the serving CCNF 302 to find the SM NF by using the NF repositoryfunction 305 will be described later with reference to FIG. 4.

When the SM NF1 303 is selected at the SM NF selection step 313, theserving CCNF 302 may transmit a PDU session request message to the SMNF1 303 at step 314 in order to set up a PDU session. The PDU sessionrequest message may contain at least one of a UE identifier such as anIMSI or a temporary ID, agreed slice assistance information, a DNN, asession ID, NSI_1 which is information about the selected network sliceinstance, or the NAS_PDU session request message.

The SM NF1 303 may select at step 315 a UP NF1 304 which is an NF for auser plane function, based on the NSI_1 received in the PDU sessionrequest message 314. The SM NF1 303 may select the UP NF1 304, based onits own network function and information about a network slice.Alternatively, the SM NF1 303 may select the UP NF1 304 by requesting anentity, such as the NF repository function 305 capable of finding anappropriate network function, to find an appropriate UP NF on the basisof the selected network slice instance information, i.e., the NSI_1. Amethod for the SM NF 303 to find the UP NF by using the NF repositoryfunction 305 will be described later with reference to FIG. 5.

The SM NF1 303 sets up a user plane for the selected UP NF1 304 at step316.

When the SM NF1 303 recognizes from the DNN that the PDU session requestof the UE is for home-routed traffic, the SM NF1 303 selects anappropriate SM NF in the home PLMN at step 317 in order to transmit thePDU session request message. The SM NF1 303 of the visited PLMN mayselect the SM NF of the home PLMN by requesting an entity, such as theNF repository function 305 of the visited PLMN capable of finding anappropriate network function, to find an appropriate SM NF on the basisof at least a part of the DNN or agreed slice assistance information.Also, when the home PLMN supports a network slice, the SM NF1 304 mayacquire together information about a network slice instance to which theselected SM NF of the home PLMN belongs. The NF repository function 305of the visited PLMN may find an appropriate SM NF and a network sliceinstance of the home PLMN to which the SM NF belongs, in the home PLMNthrough an NF repository function 308 of the home PLMN. This method willbe described later with reference to FIG. 6. Meanwhile, the SM NFselection step 317 of the home PLMN may be performed by the SM NF1 303of the visited PLMN as described above, or may be performed by theserving CCNF 302. Hereinafter, the SM NF selected in the home PLMN willbe defined and described as an SM NF2 306.

The SM NF1 303 transmits at step 318 an HR_PDU session request messageto the SM NF2 306 selected in the home PLMN in order to set up a PDUsession. The HR_PDU session request message may contain at least one ofa UE identifier such as an IMSI, agreed slice assistance information, asession ID, an address of the UP NF1 304 of the visited PLMN, orinformation of network slice instance including the SM NF2 306 of thehome PLMN acquired at the SM NF selection step 317 of the home PLMN.

When the HR_PDU session request message is received at step 318, the SMNF2 performs authorization based on an operator's policy through apolicy function 310 at step 319.

After the authorization, the SM NF2 306 assigns an IP address of the UE301 and selects an appropriate UP NF for setting up a user plane in thehome PLMN at step 320. The SM NF2 306 may send a request to an entitysuch as the NF repository function 308 of the home PLMN capable offinding an appropriate network function and retrieve the appropriate UPNF in the home PLMN, based on at least a part of the DNN or agreed sliceassistance information. Alternatively, when there is information of anetwork slice instance to which the SM NF2 306 belongs, the SM NF2 306may send a request to an entity such as the NF repository function 308of the home PLMN capable of finding an appropriate network function andretrieve the appropriate UP NF in the home PLMN, based on the networkslice instance information. A method for the SM NF2 306 to retrieve theUP NF in the home PLMN by using the NF repository function 308 of thehome PLMN will be described later with reference to FIG. 7. Hereinafter,the UP NF selected in the home PLMN will be defined and described as aUP NF2 307.

After assigning the UE IP address and selecting the UP NF in the homePLMN at step 320, the SM NF2 306 sets up a user plane for the selectedUP NF2 307 at step 321. In addition, the SM NF2 306 transmits an HR PDUsession response message containing a setup result of a PDU session tothe SM NF1 303 of the visited PLMN at step 322. The HR PDU sessionresponse message may contain at least one of the UE IP address acquiredat the step 320, a session ID, or address information of the selected UPNF2 307.

The SM NF1 303 forwards the PDU session setup result to the UE 301 viathe serving CCNF 302. Specifically, at step 323, the SM NF1 303generates a NAS_PDU session response message and transmits, to theserving CCNF 302, a PDU session response containing the NAS PDU sessionresponse message together with a UE temporary ID and the session ID. TheNAS PDU session response message may contain at least one of the agreedslice assistance information, the DNN, the UE IP address, or the sessionID. At step 324, the serving CCNF 302 forwards the NAS_PDU sessionresponse message to the UE to inform that the PDU session is generated.

FIG. 4 illustrates a process in which a serving CCNF finds anappropriate SM NF through an NF repository function at the SM NFselection step 313 of FIG. 3.

The serving CCNF 302 sends at step 313 a an NF discovery request messageto the NF repository function 305 of the visited PLMN to request findingan appropriate SM NF. The NF discovery request message may contain atleast one of SM NF information which is information about a type of NFto be found, serving CCFN information which is information about arequesting NF, a visited PLMN ID which is information about a PLMN fromwhich a requested NF will be found, or previously allocated networkslice instance information. In addition, the NF discovery requestmessage may further contain at least one of an IMSI or a temporary ID asidentification information of the UE.

In response to the request of the step 313 a, the NF repository function305 finds an appropriate SM NF by searching its database or otherdatabase and then forwards address information of the SM NF to theserving CCNF 302 at step 313 b.

FIG. 5 illustrates a process in which an SM NF1 finds an appropriate UPNF through an NF repository function at the UP NF selection step 315 ofFIG. 3.

The SM NF1 303 sends at step 315a an NF discovery request message to theNF repository function 305 of the visited PLMN to request finding anappropriate UP NF. The NF discovery request message may contain at leastone of UP NF information which is information about a type of NF to befound, SM NF1 information which is information about a requesting NF, avisited PLMN ID which is information about a PLMN from which a requestedNF will be found, or previously allocated network slice instanceinformation. In addition, the NF discovery request message may furthercontain at least one of an IMSI or a temporary ID as identificationinformation of the UE.

In response to the request of the step 315a, the NF repository function305 finds an appropriate UP NF by searching its database or otherdatabase and then forwards address information of the UP NF to the SMNF1 303 at step 315 b.

FIG. 6 illustrates a process in which an SM NF1 of a visited PLMN findsan appropriate SM NF in a home PLMN through an NF repository function atthe SM NF selection step 317 of the home PLMN of FIG. 3.

The SM NF1 303 sends at step 317a an NF discovery request message to theNF repository function 305 of the visited PLMN to request finding anappropriate SM NF in the home PLMN. The NF discovery request message maycontain at least one of SM NF information which is information about atype of NF to be found, SM NF1 information which is information about arequesting NF, a home PLMN ID which is information about a PLMN fromwhich a requested NF will be found, previously allocated network sliceinstance information if it exists, a DNN, or agreed slice assistanceinformation. In addition, the NF discovery request message may furthercontain at least one of an IMSI or a temporary ID as identificationinformation of the UE.

In response to the request of the step 317a, the NF repository function305 of the visited PLMN sends the NF discovery request message to the NFrepository function 308 of the home PLMN at step 317b. Then, the NFrepository function 308 of the home PLMN finds an appropriate SM NF bysearching its database or other database and forwards addressinformation of the SM NF to the NF repository function 305 of thevisited PLMN at step 317c. In case where the home PLMN supports anetwork slice, information about a network slice instance to which thefound SM NF belongs may be forwarded together to the NF repositoryfunction 305 of the visited PLMN. Then, the NF repository function 305of the visited PLMN forwards the received information to the SM NF1 303as response at step 317d.

FIG. 7 illustrates a process in which an SM NF2 finds an appropriate UPNF through an NF repository function at the UP NF selection step 320 ofFIG. 3.

The SM NF2 306 sends at step 320a an NF discovery request message to theNF repository function 308 of the home PLMN to request finding anappropriate UP NF. The NF discovery request message may contain at leastone of UP NF information which is information about a type of NF to befound, SM NF2 information which is information about a requesting NF, ahome PLMN ID which is information about a PLMN from which a requested NFwill be found, previously allocated network slice instance informationif it exists, a DNN, or agreed slice assistance information. Inaddition, the NF discovery request message may further contain at leastone of an IMSI or a temporary ID as identification information of theUE.

In response to the request of the step 320a, the NF repository function308 finds an appropriate UP NF by searching its database or otherdatabase and then forwards address information of the UP NF to the SMNF2 306 at step 320b.

FIG. 8 illustrates another example of a core network architectureexcluding a terminal and a base station in a network that supportsroaming between wireless communication systems applying a network sliceand also serves home-routed traffic. According to the networkarchitecture of FIG. 8, contrary to the network architecture of FIG. 1,a network slice instance for serving home-routed traffic is used throughan NSI selector in a home PLMN.

Referring to FIG. 8, a visited PLMN to which a roaming terminal willattach includes a CCNF 801 and a slice specific core network function805 that collects network functions related to a network slice. Theslice specific core network function 805 includes SSCNF 807 includingSlice CP NF 1, , Slice CP NF_n which are control plane network functionsdefined to be used only within a network slice, and SSUNF 808 includingSlice UP NF_1, . . . , Slice UP NF_n which are user plane networkfunctions defined to be used only within a network slice. The CCNF 801may include a network slice instance (NSI) selector 814 in the visitedPLMN.

The home PLMN includes a subscriber repository 803 that storessubscription information of a terminal, a home policy control function802 that controls applying a policy in the home PLMN, an AF 804 thatprovides information about the policy to the home policy controlfunction 802, and a slice specific core network function 806 thatcollects network functions related to a network slice. The slicespecific core network function 806 includes SSCNF 809 including Slice CPNF_1, . . . , Slice CP NF_n which are control plane network functionsdefined to be used only within a network slice, and SSUNF 810 includingSlice UP NF_1, . . . , Slice UP NF_n which are user plane networkfunctions defined to be used only within a network slice. The home PLMNmay include a network slice instance (NSI) selector 815 that selects anetwork slice in the home PLMN.

In addition, the core network may include a visited NF repositoryfunction 812 and a home NF repository function 813, which findappropriate network functions from network functions of the visited PLMNand the home PLMN by request. The visited NF repository function 812 maybe located within the CCNF 801. Also, the home NF repository function813 may operate as an NH selector located within the CCNF 801 andperforming a function of selecting an appropriate NF from a networkslice instance. Although this disclosure uses the term “NF repositoryfunction” for convenience of description, this may refer to an NFIselector when a network slice is used.

The CCNF 801 is connected to a terminal attaching to the visited PLMNand a base station accessed by the terminal, processes control messagesfor managing the terminal, and manages the mobility of the terminal. Inaddition, the CCNF 801 is connected to the subscriber repository 803located in the home PLMN, receives subscriber related information fromthe subscriber repository 803, and performs authentication of theterminal. Also, the CCNF 801 selects a network slice instance to beprovided to the terminal by using information of the accessing terminal,and selects an appropriate slice CP NF from the SSCNF 807 belonging tothe corresponding network slice instance. The CCNF 801 may use thevisited NF repository function 812 to select the appropriate slice CPNF. The slice CP NF selects an appropriate slice UP NF from the SSUNF808 belonging to the network slice instance. The slice CP NF may use thevisited NF repository function 812 to select the appropriate slice UPNF.

Alternatively, the CCNF 801 may select, through the NSI selector 814, anetwork slice instance to be provided to the corresponding terminal byusing information of the terminal, select a slice CP NF from the SSCNF807 belonging to the corresponding network slice instance, and select aslice UP NF from the SSUNF 808 belonging to the corresponding networkslice instance. That is, the CCNF 801 may select both the slice CP NFand the slice UP NF. Also, the CCNF 801 may use the visited NFrepository function 810 to select appropriate slice CP NF and slice UPNF.

The slice CP NF and the slice UP NF selected in the visited PLMN throughthe NSI selector 814 support a data service in a terminal-belongingnetwork slice through connection with a slice CP NF and a slice UP NFselected from the S SCNF 809 and the SSUNF 810 selected through the NSIselector 815 belonging to the home PLMN.

In case of generating a PDU session for home-routed traffic in thenetwork architecture of FIG. 8, procedures similar to those of FIG. 3are performed. However, at the subscription data check step 312, theserving CCNF 302 transmits at least one of a home PLMN ID, DNNinformation, or agreed slice assistance information to the NSI selectorof the visited PLMN in order to request an appropriate network sliceinstance value of the home PLMN. The NSI selector of the visited PLMNforwards information received from the serving CCNF 302 to the NSIselector of the home PLMN. The NSI selector of the home PLMN selects anappropriate network slice instance, based on the above information, andforwards the selected network slice instance to the serving CCNF 302. Inaddition, the network slice instance information NSI 2 of the selectedhome PLMN is forwarded to the SM NF1 via the PDI session request 314 andmay be used at step 317 of selecting the SM NF of the home PLMN.

FIG. 9 is a diagram illustrating a structure of a terminal according toan embodiment of the disclosure.

Referring to FIG. 9, the terminal may include a transceiver 910, acontroller 920, and a storage 930. In the disclosure, the controller 920may be defined as a circuit, an application specific integrated circuit,or at least one processor.

The transceiver 910 may transmit and receive signals to and from othernetwork entities. For example, in a network initial connection andregistration procedure of the terminal in a roaming environment to whicha network slice is applied as shown in FIG. 2, the transceiver 910 maytransmit an initial attach request message to a base station (step 211)or receive an initial attach accept message from the base station (step219). Also, in a process in which the terminal generates a PDU sessionfor home-routed traffic in a roaming environment to which a networkslice is applied as shown in FIG. 3, the transceiver 910 may transmit aPDU session request message to a serving CCNF (step 311) or receive aPDU session response message from the serving CCNF (step 324).

The controller 920 may control the overall operation of the terminalaccording to embodiments of the disclosure. For example, the controller920 may control signal flows between respective blocks to performoperations according to flowcharts described above. In particular, thecontroller 920 may control operations disclosed herein for attachmentand home-routed PDU session generation of the terminal according toembodiments of the disclosure. In an embodiment, the controller 920 maybe configured to control the transceiver 910 to transmit a PDU sessionrequest message, which contains slice assistance information indicatingthe characteristics of a service that the terminal desires to use, to aCCNF of a visited PLMN, and also control the transceiver 910 to receivea PDU session response message containing an IP address of the terminalfrom the CCNF of the visited PLMN.

The storage 930 may store at least one of informationtransmitted/received through the transceiver 910 and informationgenerated through the controller 920. For example, the storage 930 maystore information for identifying the terminal, slice selectionassistance information, and the like.

FIG. 10 is a diagram illustrating a structure of a CCNF according to anembodiment of the disclosure.

Referring to FIG. 10, the CCNF may include a transceiver 1010, acontroller 1020, and a storage 1030. In the disclosure, the controller1020 may be defined as a circuit, an application specific integratedcircuit, or at least one processor.

The transceiver 1010 may transmit and receive signals to and from othernetwork entities. For example, in a network initial connection andregistration procedure of a terminal in a roaming environment to which anetwork slice is applied as shown in FIG. 2, the transceiver 1010 mayreceive an initial attach request message from a base station (step 212)or transmit an initial attach accept message to the base station (step218). Also, in a process in which the terminal generates a PDU sessionfor home-routed traffic in a roaming environment to which a networkslice is applied as shown in FIGS. 3 and 4, the transceiver 1010 mayreceive a PDU session request message from the terminal (step 311),transmit the PDU session request message to an SM NF1 (step 314),receive a PDU session response message from the SM NF 1 (step 323),transmit the PDU session response message to the terminal (step 324),transmit an NF discovery request message to an NF repository function(step 313 a), or receive an NF discovery response message from the NFrepository function (step 313 b).

The controller 1020 may control the overall operation of the CCNFaccording to embodiments of the disclosure. For example, the controller1020 may control signal flows between respective blocks to performoperations according to flowcharts described above. In particular, thecontroller 1020 may control operations disclosed herein for attachmentand home-routed PDU session generation of the terminal according toembodiments of the disclosure. In an embodiment, the controller 1020 maybe configured to control the transceiver 1010 to receive a PDU sessionrequest message, which contains slice assistance information indicatingthe characteristic of a service that the terminal desires to use, fromthe terminal, to transmit a first discovery request message containing ahome PLMN ID of the terminal and the slice assistance information to anNF repository function, and to receive a first discovery responsemessage containing an address of an SF NF of the home PLMN from the NFrepository function.

The storage 1030 may store at least one of informationtransmitted/received through the transceiver 1010 and informationgenerated through the controller 1020. For example, the storage 1030 maystore an ID of a terminal, a home PLMN ID of the terminal, sliceselection assistance information, an IP address of the terminal, and thelike.

In the above-described embodiments of the disclosure, various elementsare expressed in singular or plural forms. However, such singular orplural forms are merely selected for the sake of convenience ofdescription and not intended to limit the disclosure. Any elementexpressed in a plural form may refer to a singular element, and viceversa.

While the disclosure has been described in detail with reference tospecific embodiments thereof, various changes and modifications may bemade without departing from the scope of the disclosure. Therefore, thescope of the disclosure should not be limited to the describedembodiments, but should be determined by the scope of the appendedclaims and equivalents.

1. A method performed by a first network repository function (NRF)entity in a first public land mobile network (PLMN), the methodcomprising: receiving, from a terminal in the first PLMN, a firstnetwork function (NF) discovery request message including an identifierof a second PLMN; transmitting, to a second NRF entity in the secondPLMN, a second NF discovery request message based on the identifier ofthe second PLMN; and receiving, from the second NRF entity, a first NFdiscovery response message including an address of a target NF in thesecond PLMN; and transmitting, to the terminal, a second NF discoveryresponse message including the address of the target NF.
 2. The methodof claim 1, wherein the first NF discovery request message includes atleast one of NF types of the target NF and the terminal, network sliceinstance information, network slice assistance information, data networkname, or an identifier of the terminal.
 3. The method of claim 1,wherein the second NF discovery response message includes network sliceinstance information. 4-5. (canceled)
 6. A first network repositoryfunction (NRF) entity in a first public land mobile network (PLMN), thefirst NRF entity comprising: a transceiver for transmitting andreceiving signals; and a controller coupled with the transceiver andconfigured to: receive, from a terminal in the first PLMN via thetransceiver, a first network function (NF) discovery request messageincluding an identifier of a second PLMN, transmit, to a second NRFentity in the second PLMN via the transceiver, a fsecond NF discoveryrequest message based on the identifier of the second PLMN, receive,from the second NRF entity via the transceiver, a first NF discoveryresponse message including an address of a target NF in the second PLMN,and transmit, to the terminal via the transceiver, a second NF discoveryresponse message including the address of the target NF.
 7. The firstNRF entity of claim 6, wherein the first NF discovery request messageincludes at least one of NF types of the target NF and the terminal,network slice instance information, network slice assistanceinformation, data network name, or an identifier of the terminal.
 8. Thefirst NRF entity of claim 7, wherein the second NF discovery responsemessage includes network slice instance information. 9-10. (canceled)11. A method performed by a terminal in a first public land mobilenetwork (PLMN), the method comprising: transmitting, to a first networkrepository function (NRF) entity in the first PLMN, a first networkfunction (NF) discovery request message including an identifier of asecond PLMN; and receiving, from the first NRF entity, a first NFdiscovery response message including an address of a target NF in thesecond PLMN, wherein a second NF discovery request message istransmitted from the first NRF entity to a second NRF entity in thesecond PLMN based on the identifier of the second PLMN, and wherein theaddress of the target NF is received in a second NF discovery responsemessage from the second NRF entity in response to the second NF requestmessage.
 12. A terminal in a first public land mobile network (PLMN),the terminal comprising: a transceiver for transmitting and receivingsignals; and a controller coupled with the transceiver and configuredto: transmit, to a first network repository function (NRF) entity in thefirst PLMN via the transceiver, a first network function (NF) discoveryrequest message including s an identifier of a second PLMN, and receive,from the first NRF entity via the transceiver, a first NF discoveryresponse message including an address of a target NF in the second PLMN,wherein a second NF discovery request message is transmitted from thefirst NRF entity to a second NRF entity in the second PLMN based on theidentifier of the second PLMN, and wherein the address of the target NFis received in a second NF discovery response message from the secondNRF entity in response to the second NF discovery request message. 13.The method of claim 11, wherein the first NF discovery request messageincludes at least one of NF types of the target NF and the terminal,network slice instance information, network slice assistanceinformation, data network name, or an identifier of the terminal. 14.The method of claim 11, wherein the first NF discovery response messageincludes network slice instance information.
 15. The terminal of claim12, wherein the first NF discovery request message includes at least oneof NF types of the target NF and the terminal, network slice instanceinformation, network slice assistance information, data network name, oran identifier of the terminal.
 16. The terminal of claim 12, wherein thefirst NF discovery response message includes network slice instanceinformation.
 17. A method performed by a first network repositoryfunction (NRF) entity in a first public land mobile network (PLMN), themethod comprising: receiving, from a second NRF entity in a second PLMN,a network function (NF) discovery request message; identifying anaddress of a target NF in the first PLMN based on the NF discoveryrequest message; and transmitting, to the second NRF entity, an NFdiscovery response message including the address of the target NF. 18.The method of claim 17, wherein the NF discovery request messageincludes at least one of NF types of the target NF and a terminal,network slice instance information, network slice assistanceinformation, data network name, or an identifier of the terminal. 19.The method of claim 17, wherein the NF discovery response messageincludes network slice instance information.
 20. A first networkrepository function (NRF) entity in a first public land mobile network(PLMN), the first NRF entity comprising: a transceiver for transmittingand receiving signals; and a controller coupled with the transceiver andconfigured to: receive, from a second NRF entity in a second PLMN viathe transceiver, a network function (NF) discovery request message,identify an address of a target NF in the first PLMN based on the NFdiscovery request message, and transmit, to the second NRF entity viathe transceiver, an NF discovery response message including the addressof the target NF.
 21. The first NRF entity of claim 20, wherein the NFdiscovery request message includes at least one of NF types of thetarget NF and a terminal, network slice instance information, networkslice assistance information, data network name, or an identifier of theterminal.
 22. The first NRF entity of claim 20, wherein the NF discoveryresponse message includes network slice instance information.